Rotor-stator gear set in a hydraulic motor-pump device



Aug. 12, 1969 N, w rr JR 3,469,481

ROTOR-STA'I'OR GEAR SET IN A HYDRAULIC MOTOR-PUMP DEVICE Filed Sept. 27,196? INVENTOR. //04/$ l Vx/va w y TTORNEYS United States Patent3,460,481 ROTOR-STATUE GEAR SET IN A HYDRAULEC MOTOR-PUMP DEVICE HollisN. White, Jr., West Lafayette, ind, assignor to TRW Inc., Cleveland,Ohio, a corporation of Ohio Filed Sept. 27, 1967, Ser. No. 670,915 Int.Cl. F04c 1/06, 1/12 U.S. Cl. 103-126 8 Claims ABSTRACT OF THE DISCLOSUREA rotor-stator gear set for a fluid pressure device of the gerotor typewhich can be used both as a motor and as a pump. The stator includes astator ring having a plurality of pockets and a corresponding pluralityof cylindrical vanes rotatably carried in the pockets for working ingear relation with the rotor to provide alternately expanding andcontracting fluid chambers between the stator and the rotor as the rotormoves hypocycloidally within the stator. The diameters of the vanes toprovide hydrodynamic oil film spaces between the vanes and the walls ofthe pockets. The stator ring is made of sintered or cast iron and thewalls of the pockets are lined with a thin layer it impervious or oilimpenetrable material to ensure the hydro dynamic oil film. Theimpervious material has a low coefficient of friction and is less hardthan is the material of which the vanes are constructed so that highpoints on the impervious liner are worn off under load. The liner may bemade of a sprayed or baked-on fluorocarbon resin or may comprise acopper plate. It the stator ring is made of sintered iron it may beplastic impregnated to render it fluid impervious.

Background of the invention This invention pertains generally to thefiled of fluid motor-pump units and more particularly to such unitswhich employ stator-rotor gear sets generally referred to in the art asgerotors.

Motonpump hydrualic devices of the gerotor type are useful in a varietyof applications where low speed, high torque rotary drives are requiredsuch as augers, conveyors, vehicle Wheel drives, etc., and comprise aninternally toothed or lobed stator and an externally toothed rotor whichis positioned eccentrically within the stator. The stator has a greaternumber of teeth or lobes than does the rotor and as the stator and therotor are rotated relative to one another the rotor moves through ahypocycloidal curve to form alternately expanding and contractingchambers between each pair of adjacent teeth of the internally toothedstator and each tooth of the rotor.

Because of the peculiar construction and operation of gerotor type gearsets the machining operations of the stator and the rotor heretoforerequired very close tolerances which, of course, increased the cost ofproduction. Furthermore because of the substantial pressures to whichthe gerotor may be subjected the stator and the rotor were generallymade of metal having high strength characteristics but also havingrelatively high coefficients of friction, thereby increasing the powerlosses within the gerotor as well as increasing the operatingtemperature and the heat transferred to the fluid operating or beingpumped by the gerotor.

An object of the present invention is not only to improve the operatingand performance characteristics of gerotors but also to reduce theproduction costs by minimizing difficult close-tolerance machining ofthe stator and by utilizing materials of construction which improve themanufacturing costs.

See

Summary of the invention With this object and others in view, thepresent invention may be summarized as comprising a hydrostatic deviceof the gerotor type including a rotor and a stator wherein the statorcomprises a stator ring having an inner peripheral wall, a plurality offragmentally cylindrically shaped walls opening to the inner peripheralWall and forming a corresponding plurality of radially spaced pocketsand a corresponding plurality of cylindrically shaped vanes providingteeth or lobes carried in the pockets for cooperating in gear relationwith the teeth of the rotor. The diameters of the pocket walls arelarger than the diameters of the vanes whereby the vanes are journalledfor rotation within the pockets and whereby a hydrodynamic oil filmspace is provided between the walls of the pockets and the vanes as therotor moves hypocycloidally within the stator.

In operation the rotor engages and makes actual contact only with thosevanes situated on one side of a diametrical line which intersects theaxis of the rotor moves hypocycloidally in the stator. The remainingvanes are engaged by the rotor and a torque applied by the rotor to theengaged vanes rotates these vanes within their respective pockets,thereby substantially reducing friction losses between the teeth of therotor and the vanes.

The present invention also features novel combinations of materials ofconstruction to further reduce friction losses, to increase performance,to reduce wear and to lengthen the useful life of the device. The vanesare made of metal of a given hardness and the walls of the pockets whichjournal the vanes are lined with a thin layer of material which not onlyhas a low coeificient of friction but which has a hardness less than thehardness of the vanes whereby high points formed on the pocket wallswill wear off under load and the contours of the pocket Walls willconform to the contours of the vanes. The pocket liner material may bemetal such as copper or may be plastic such as fluorocarbon resin, bothof which have a low coefiicient of friction and both of which areimpervious to maintain the hydrodynamic oil film between the vanes andthe walls of the pockets.

The stator ring may be formed in a molding operation using cast iron ormay be sintered iron formed in a stamping and sintering operation aswill be understood by those skilled in the art. In the latterconstruction the sintered iron may be plastic impregnated to render thestator ring impervious and to prevent dissipation of the hydrodynamicoil film between the pocket walls and the vanes.

Many other features, advantages and additional objects of the presentinvention will becorne' manifest to those versed in the art upon makingreference to the detailed description which follows and the accompanyingsheets of drawings in which preferred structural embodimentsincorporating the principles of the present invention are shown by Wayof illustrative example only.

Brief description of the drawing FIGURE 1 is an elevational view of agear set of the gerotor type for functioning as a fluid pump or as afluid motor and constructed in accordance with the principles of thepresent invention.

FIGURE 2 is a greatly enlarged and fragmentary crosssectional view ofone embodiment of a stator vane and an adjacent portion of the statorring.

FIGURE 3 is similar to FIGURE 2 but illustrates another embodiment ofthe invention.

Description of the preferred embodiments A fluid pressure devicecomprising a gear set of the gerotor type for functioning as a fluidpump and as a fluid motor and constructed in accordance with theprinciples 3 of the present invention is indicated generally atreference numeral in FIGURE 1. The device 10 may be more particularlycharacterized as comprising an internally toothed stator 11 and anexternally toothed rotor 12.

The teeth or lobes of the rotor 12 comprise convexlyshaped portions 13angularly spaced about a central axis of the rotor and separated byconcavely-shaped portions formed in an outer wall 16 of the rotor. Theteeth of the stator 11 comprise a plurality of angularly spacedcylindrically shaped members or vanes 17 which are housed in acorresponding plurality of fragmentally cylindrically shaped wallsforming recesses or pockets 18 opening to an inner peripheral wall 19 ofan annularly shaped stator ring member 20.

The number of teeth of the rotor 12 is preferably one less than thenumber of teeth of the stator 11. In the embodiment illustrated therotor 12 has a total of six teeth while the stator 11 has one more thanthe rotor or seven teeth.

The axis of the rotor 12 is eccentrically disposed with respect to acentral axis of the stator 11 and as the rotor 12 is rotated relative tothe stator 11 the rotor teeth 13 mesh with the stator teeth or vanes 17to impart a hypocycloidal path of movement to the rotor 12 whereby itorbits about the central axis of the stator six times, corresponding tothe number of teeth of the rotor 12, for each revolution of the rotor12.

During this hypocycloidal movement of the rotor 12 the teeth or lobes 13thereof form, in combination with the teeth 17 of the stator 11 and theinner peripheral wall 19 of the stator ring 20, alternately expandingand contracting fluid chambers indicated respectively at referencenumerals 21a-21g. In other words, assuming that the rotor 12 is beingrotated about its central axis in the direction indicated by the arrowat reference numeral 22, the fluid chamber 21:: has contracted to itsminimum volume and further rotation of the gear 12 will have the effectof expanding the volume of this chamber. Chamber 21b is approaching itsminimum volume and chambers 21c and 21d are being contracted. Chambers21e, 21f and 21g are expanding and of course further rotation of therotor 12 from the position thereof shown in FIGURE 1 will have theeffect of also expanding chamber 21a.

When the device 10 is being utilized as a fluid motor means are providedfor communicating the expanding fluid chambers to a source ofpressurized fluid and the contracting chambers are communicated with adischarge or an outlet opening. When the device 10 is being utilized asa pump the expanding chambers are placed in communication with a fluidinlet and the contracting chambers comprise the high pressure chambersand are placed in communication with a pump discharge or outlet opening.Suitable means for communicating the fluid chambers alternately andsuccessively with the fluid inlet and outlet openings are known in theart and are disclosed, for example, in Hollis N. White, Jr. et al. US.Patent No. 3,288,034.

Although the externally toothed rotor 12 is described herein as beingrotatable within and orbitally movable relative to the internallytoothed enveloping stator 11, either member can be fixedly arrangedrelative to the other. Furthermore, one member can be arranged to rotateonly while the other member orbits only, as will be understood by thoseskilled in the art. Thus the rotor 12 may be a fixed member and thestator 11 a movable member as desired.

In the illustrated embodiment of the invention the teeth 13 and theinterconnecting arcuately shaped surface 14 of the rotor 12 and thevanes 17 of the stator 11 are constructed and arranged so that the rotor12 only contacts those of the vanes 17 which are disposed on one side ofa diametrical line which intersects the central axis of the rotor 12 aswell as that particular chamber, such as chamber 21a in the arrangementof parts shown in FIGURE 1, which has contracted to its minimum volume.In FIG- URE 1 such diametrical line is indicated in broken lines atreference numeral 22. Thus the teeth 13 which form the contractingchambers 21b, 21c and 21d are in engagement with their correspondingvanes 17 in the relative positions of the stator 11 and the rotor 12shown in FIG- URE 1, whereas the rotor teeth partially forming theexpanding chambers 212, 21f and 21g are in slightly spaced relation withtheir corresponding vanes 17.

In this disposition and direction of rotation of the parts shown inFIGURE 1, the vane 17 will rotate counterclockwise due to the vaneaction. Vanes adjacent to chambers 21b, 21c and 21d will rotate if thedevice is being used as a motor. Vanes adjacent to the chambers 21g, 21and He will rotate if the device is being used as a pump.

The diameters of the pocket or recess walls 18 are greater than thediameters of the vanes 17, as a consequence of which the vanes arecapable of moving slightly not only toward the axis of the stator ring20 but from side to side. The teeth 13 of the rotor 12 are constructedand arranged to permit such movement of the vanes as the rotor 12rotates and orbits within the stator 11 and as a consequence theperipheral surfaces of the vanes 17 are urged slightly away from thepocket walls 18 by the pressure of the operating fluid such as oil,thereby providing a hydrodynamic oil filrn between the vanes 17 and thepockets 18. The film not only increases the performance characteristicsof the device 10 by reducing the frictional forces between the vanes andthe pockets and thus reducing the power losses of the rotor 12, but alsoby reducing wear and increasing the overall operating life of the device10.

The spacing between the walls of the vanes indicated in FIGURE 1 atreference numeral 17' and 17" and the walls of their respective pocketshas been greatly exaggerated merely to illustrate this hydrodynamic oilfilm space.

One aim of the present invention as mentioned heretofore is to reducemanufacturing costs by reducing the requirements of close tolerancemachining. According to the present invention the stator ring 20 isformed of cast iron in a casting operation or is formed of sintered ironin an operation involving the process of compacting powdered metal in adie under pressure and then heating the pressed powder in a sinteringoperation. Both of these manufacturing techniques are known andunderstood by those skilled in the art.

FIGURES 2 and 3 are greatly enlarged representations of that portion ofa vane 17 and of the stator ring 20 encircled in the dot-dashed lineindicated at reference numeral 26 in FIGURE 1. FIGURE 2 illustrates anembodiment of the present invention utilizing a cast iron stator ring 20whereas in FIGURE 3 the stator ring is made of sintered iron.

In accordance with the principles of this invention, after the statorring 20 has been cast or sintered the pocket walls 18 are lined with athin layer of another material such as plastic or copper. The purposesof the liner are at least threefold: (1) to obviate close machining ofthe pocket walls 18 in order to have good bearing surfaces for the vanes17; (2) to increase performance of the hydrostatic device 10 by reducingfrictional losses between the vanes 17 and the stator ring 20 and (3) tomaintain the hydrodynamic oil film between the adjacent peripheral wallsof the vanes 17 and the pocket Walls 18.

To achieve these goals the liner or coating of material applied to thepockets of the cast or sintered iron stator rings 20 is constructed ofmaterial having a hardness which is less than the hardness of the metalvanes 17 whereby irregular contours and high points of the liner aresmoothed under the load of the vane to conform to the vane contour. Theliner material is also chosen because of its low coeflicient offriction, thereby reducing frictional forces and wear of the liner.Furthermore the liner material is impervious to fluid as a consequenceof which the hydrodynamic oil film between the vanes 17 and the pocketwalls 18 mentioned hereinabove is sustained.

In FIGURE 2 the material of which the stator ring 20 is constructed iscast iron and the extremities of the pocket wall formed in the statorring 20 and facing the metal vane 17 are indicated at reference numerals18a. The liner material which covers the cast iron and which forms thebearing surface for the vane 17 is indicated at reference numeral 27.

In the embodiment of the invention illustrated in FIG- URE 2 the linermaterial 27 is plastic fluorocarbon resin. Fluorocarbon resins areclassified as thermoset-plastics, and are chemically analogous to thepolyolefins, but with some or all of the hydrogen atoms replaced byfluorine atoms.

Fluorine substitution generally contributes to: (1) chemical inertness;(2) resistance to high and low temperatures; (3) essentially zeromoisture absorption; (4) low coeflicient of friction; (5)non-flammability and (6) weather and oxidation resistance.

-It is recognized that at least four classes of fluorocarbon resin arenow commercially available. For example, polytetrafluoroethylene, whosebasic unit consists of two carbons with fluorine fully substituting forhydrogen, represents one class of fluorocarbon resin which is suppliedby E. I. du Pont de Nemours & Co., Inc., under the trade name Teflon andby Allied Chemical Corporation under the trade name Halon.

Polymeric fluorinated ethylene propylene, a copolymer ofpolytetrafluoroethylene and hexafluoropropylene, is also supplied by E.I. du Pont de Nemours & Co., Inc., under the trade name Teflon F -E P."

Polymeric chlorotrifluoroethylene is another resin which, in a strictsense, might be referred to as a chlorofluorocarbon, however, typical ofa material in this case is that supplied by Minnesota Mining andManufacturing Co., under the trade name KEL-F8l. Copolymers of that typemodified with small amounts of vinylidene fluoride and other fluorinecontaining monomers to improve processability are also available. Suchresins include the materials supplied by Allied Chemical Corporationunder the trade name Plaskon as well as KEL- F82 supplied by MinnesotaMining and Manufacturing Co.

Lastly, polyvinylidene fluoride is another resin supplied by PennsaltChemical Corp. under the trade name Kynar.

By using a plastic fluorocarbon resin such as Teflon, machining of thecast iron (or sintered iron) walls of the pockets 18 is obviated sincesuch plastic exhibits resiliency characteristics and is less hard thanis the steel vane 18. Thus any irregularities in the liner material 27and out-of-flatness spots or high points are flattened and smoothed bythe vane 17 whereby the surface of the liner 27 assumes the contour ofthe vane 17.

Furthermore because of the low coeflicient of friction of plasticfluorocarbon resin, wear on the liner as well as on the vane is reducedand the operating and performance characteristics of the hydrostaticdevice 10 are increased. Since the plastic is impenetrable by fluid theliner 27 is able to maintain the hydrodynamic oil film between the linerand the vane 17, even under high fluid pressures.

In FIGURE 3 the liner material is indicated at reference numeral 27a andin this embodiment is made of copper which has been plated to the statorring 20. The material of which stator ring 20 is constructed in FIG- URE3 is sintered iron but the principles of the present invention alsocontemplate the application of copper plate to cast iron. In otherwords, the liner of plastic fluorocarbon resin indicated at referencenumeral 27 in FIGURE 2 and the liner of copper plating indicated atreference 27a in FIGURE 3 can both be applied to either the cast ironstator ring indicated at 20a in FIGURE 2 v6 or the sintered iron statorring indicated at 20a in FIG- URE 3.

Since the hardness of the vane 17 is greater than the hardness of thecopper plate 27a the surface of the copper will smooth under load toconform to the contour of the vane 17. In addition one of the salientcharacteristics of copper is its low coefficient of friction and it is,of course, impervious to fluids whereby the hydrodynamic oil filmbetween the liner 27a and the vane 17 is maintained.

With respect to the hydrodynamic oil film, in the embodiment of theinvention wherein the stator ring 20 is constructed of cast iron,because of the imperviousness of cast iron the oil film is sustainedbetween the walls of the vanes 17 and the pockets 18 since the oilcannot leak out of the chambers 21a-21g through the body of the statorring 20.

On the other hand sintered iron, because of its porosity, is pervious tofluids and leakage of oil from the chambers 21a-21g can occur throughthe body of the stator ring 20. For that reason the present inventioncontemplates an impregnation of the sintered iron stator ring 20a withplastic, thereby rendering the ring 20a, including peripheral wall 19which partially forms the chambers 21a- 21g, impervious to the oil andensuring the maintenance of oil in the chambers 21a-21g and of thehydrodynamic oil film between the vanes 17 and the pockets 18.

Although minor modifications might be suggested by those versed in theart it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably comewithin the scope of my contribution to the art.

I claim as my invention:

1. A fluid pressure device comprising a gear set having a pair ofrelatively movable internally and externally toothed members,

said internally toothed member comprising a ring having an innerperipheral wall,

a plurality of circumferentially spaced recesses in said ring opening tosaid inner peripheral wall, and

a corresponding pluraity of complementarily shaped vanes carried in saidrecesses and cooperating in gear relation with said externally toothedmember, said vanes being slightly undersized with respect to saidrecesses for providing a hydrodynamic oil film between the walls thereofand being rotatable and slightly radially sbiftable in said recesses formovement in response to operation of said gear set, the walls of saidrecesses being lined with bearing material having a lower coeflicient offriction than said ring, having a hardness less than said vanes andbeing impervious to oil.

2. The fluid pressure device as defined in claim 1 wherein said ring isconstructed of cast iron, the liner of the walls of the recessescomprises copper which is plated to the cast iron ring.

3. The fluid pressure device as defined in claim 1 wherein said ring isconstructed of cast iron, the liner of the walls of the recessescomprises a coating of plastic fluorocarbon resin on the cast iron.

4. The fluid pressure device as defined in claim 3 wherein saidfluorocarbon resin is selected from a class consisting ofpolytetrafluoroethylene, polymeric fluorinated ethylene propylene,polymeric chlorotrifluoroethylene and polyvinylidene fluoride.

5. A fluid pressure device comprising a gear set having a pair ofrelatively rotatably and orbitally movable internally and externallytoothed members,

said internally toothed member comprising a ring having an innerperipheral wall,

a plurality of circumferentially spaced recesses in said ring opening tosaid inner peripheral wall, and

a corresponding plurality of complementarily shaped vanes carried insaid recesses and cooperating in gear relation with said externallytoothed member,

7 said ring being constructed of plastic impregnated oil impervioussintered iron, References Cited the walls of said recesses being linedwith bearing mate- UNITED STATES PATENTS rial having a lower coefficientof friction than said 2 345 975 4/1944 Herman sintered iron ring.

6. The fluid pressure device as defined in claim 5 where- 5 25869642/1952 l in the liner ofthe walls of the recesses comprises cop- 261904011/1952 Malschper which is plated to the sintered iron ring. 2815'71812/1957 Avery- 7. The fluid pressure device as defined in claim 53289602 12/1966 Hudgens' wherein the liner of the walls of the recessescomprises 10 3389618 6/1968 McDermott 103 130 a plastic fluorocarbonresin.

8. The fluid pressure device as defined in claim 7 D ONLEY STOCKINGP'nmary Examiner wherein said fluorocarbon resin is selected from aclass WILBUR J. GOODLIN, Assistant Examiner consisting ofpolytetrafluoroethylene, polymeric fluorinated ethylene propylene,polymeric chlorotrifluoroethyl- 15 US. Cl. X.R. ene and polyvinylidenefluoride. 103130, 216

